1. Field of the Invention
This invention relates to a solar water heater of natural circulation type, and more particularly to an improved water heater of the kind above described in which the heat collection efficiency of a heat collector disposed in inclined relation on the roof or any other suitable location of a house can be increased especially in the winter season while maintaining the same substantially equivalent to that of prior art ones in the summer season.
2. Description of the Prior Art
A prior art solar water heater of natural circulation type has a structure as shown in FIG. 1. Referring to FIG. 1, a heat collector 1 is disposed in inclined relation on the roof or any other suitable location of a house and is connected by conduits 3 and 4 to a hot-water reservoir 2 disposed at a higher level. The energy of solar radiation incident upon the water heater is converted into heat by the heat collector 1 to heat water circulating between the heat collector 1 and the hot-water reservoir 2 thereby decreasing the density of water. As a result, heated water flows upward into the hot-water reservoir 2 through the conduit 4, and at the same time, water of lower temperature in the lower part of the hot-water reservoir 2 flows downward into the heat collector 1 through the conduit 3. In this manner, water continues to circulate between the heat collector 1 and the hot-water reservoir 2 so long as the solar radiation persists and the temperature difference exists between the heat collector 1 and the hot-water reservoir 2. Water ceases to circulate when the solar radiation disappears due to sunset.
As shown in FIG. 1, the hot-water reservoir 2 is connected to a source of water (not shown) by a water feed conduit 5 which is provided at the end thereof with a ball tap 6 floating on the water level in the hot-water reservoir so that water of constant volume can be contained always within the hot-water reservoir 2. The heat collector 1 comprises metal sheets or heat collecting sheets 7 defining a plurality of water circulation passages therein. These heat collecting sheets 7 are covered at the front or heat collecting surface thereof with a glass plate 8, and the remaining portions of the heat collecting sheets 7 are covered with a layer of heat insulating material 9.
In such a prior art solar water heater of natural circulation type, however, the temperature of hot water in the reservoir 2 is not raised sufficiently in the winter season due to the fact that the temperature of feed water is lower than that in the other seasons and the amount of solar radiation is also less than that in the other seasons. It has therefore been necessary to provide a gas or oil burner for applying additional heat to hot-water supplied from the reservoir 2 to, for example, a bath so that the bath can be satisfactorily used in the winter season. (The heating of hot-water by the gas burner is commonly called supplemental heating.) Thus, the merit of the solar water heater has been considerably lost in the winter season.
The temperature of water heated by the heat collector can be raised by increasing the heat collecting efficiency per unit area of the heat collector or by enlarging the overall area of the heat collecting surface. However, the former method is defective in that there is a limit in the increase in the heat collecting efficiency, and the latter method is also defective in that mere enlargement of the heat collecting area results in an enlarged volume of the water heater and heat more than that required will be collected in the summer season. Thus, both these methods are not best in any way.